|Publication number||US7054643 B2|
|Application number||US 10/079,338|
|Publication date||May 30, 2006|
|Filing date||Feb 20, 2002|
|Priority date||Feb 20, 2002|
|Also published as||US20030157899, WO2003071817A1|
|Publication number||079338, 10079338, US 7054643 B2, US 7054643B2, US-B2-7054643, US7054643 B2, US7054643B2|
|Inventors||Dirk Trossen, Hemant M. Chaskar|
|Original Assignee||Nokia Corporation|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (12), Non-Patent Citations (3), Referenced by (27), Classifications (43), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to providing multicast services in a wireless communications system.
Multimedia streaming is considered to be a major evolving Internet application since it aims at replacing widely known television applications such as video-on-demand, pay-per-view, or video broadcast. Currently, a number of portal sites offer Internet protocol (IP) multicast services to be extended using wireless transmission to wireless terminals. With such a service, a wireless system broadcasts data packets to a plurality of wireless terminals. Each wireless terminal receives and processes the same stream of packets. Using multicast transmission rather than a plurality of unicast transmissions is substantially more spectrum efficient providing that the services are amenable to broadcasting to the plurality of wireless terminals. Because frequency spectrum for wireless services is very limited and very expensive to expand, the utilization of multicast services is very appealing to wireless service providers.
An example of a multicast service is IP multicast streaming for news and entertainment content in audio and video formats. As the data rate of wireless channels continues to increase and as the wireless channels are becoming optimized for IP packet transfers as with cdma2000 1.25 MHz Evolution (1×EV) 3GPP2 wireless standards, an increasing number of wireless customers will have access to multicast services. If the service were provided with a dedicated communications link between a base station and each wireless terminal in the same geographical area (corresponding to a cell that is served by the base station), the frequency spectrum usage essentially increases proportionally to the number of wireless terminals that subscribe to the service. This approach is not efficient in that data transmission is duplicated for the participating wireless terminals. Multicast services broadcast the data stream to all the participating wireless terminals on the wireless downlink (base station to wireless terminals), eliminating the duplication of data transmission and thus improving the frequency spectrum efficiency of the wireless channels.
Typically, multicast services are inherently unidirectional from the wireless base station to the wireless terminal. As an example, a video service may require a transmission rate of several hundred thousand bits per second in the forward direction and several hundred bits per second in the reverse direction in order to support signaling. Because of the pronounced asymmetry of transmission, the quality of the received signal at the wireless terminal is an important parameter in supporting multicast services. In the prior art, substantial time delays are incurred with having rate control functionality at the wireless terminal rather than the wireless infrastructure and the IP core network. With dynamic radio conditions that are typical with wireless communications, these delays can result in data transmission loss resulting in a degradation of services. Reducing associated delays will improve the quality of multicast services that are provided by wireless communications systems.
The present invention provides methods and apparatus for transmitting multicast content over a wireless channel. At least one wireless terminal requests a multicast service that may comprise a number of layers. A wireless infrastructure comprising a base station and a node determines a data rate that the at least one wireless terminal can receive reliably and correspondingly configures a multicast session for at least one layer. The node utilizes measurements provided by the wireless terminal. The node through the base station signals the wireless terminal about a link-level multicast address corresponding to a time slot for which the wireless terminal shall process packets. An associated point of attachment with a core data network controls a data flow from a multicast content source through the core data network in order to match the data rate over the wireless channel.
In an exemplary embodiment of the invention, a wireless communications system comprises a plurality of wireless terminals, a base station, a node, an Internet protocol (IP) peer, and an IP core network. The exemplary embodiment utilizes signaling between a wireless terminal to an IP peer through a serving base station for requesting subscription to a multicast group corresponding to a multicast service. The wireless terminal can be one of a plurality of wireless terminals that is receiving the multicast service. In the exemplary embodiment, the wireless terminal also sends bandwidth requirements for each layer (corresponding to a multicast group address). In a variation of the exemplary embodiment, the IP peer supports a data structure that associates the bandwidth requirement with each layer of the multicast service. The wireless terminal also notifies the node about a signal to noise ratio (SNR) measurement. The node consequently schedules packets for each layer on the wireless channel and notifies the IP peer about the transmitted layers to the wireless terminal. The IP peer adjusts the packet flow through the IP core network in order to adapt to the number of layers that is being transmitted over the wireless channel to the plurality of wireless terminals.
In another embodiment of the invention, a wireless communications system combines the functionality of a node and an IP peer into a base station. The incorporation of an IP router facilitates an all-IP network for wireless multicast services.
A more complete understanding of the present invention and the advantages thereof may be acquired by referring to the following description in consideration of the accompanying drawings, in which like reference numbers indicate like features and wherein:
In the following description of the various embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope of the present invention.
Wireless channel 102 transports data in the forward direction (base station to wireless terminal) and the reverse direction (wireless terminal to base station). Typically, for a multicast service, a data rate on the forward direction is substantially greater than a data rate on the reverse direction. In the example, wireless communications channel 102 has sufficient bandwidth to transport a data stream with the audio component and both video components. However, a wireless terminal (as requested by a user) may not wish to totally experience the broadcast. Also, the wireless terminal may not have the capability of processing the entire data stream because the wireless terminal lacks a display capability (e.g. does not have a video display). Moreover, the wireless propagation characteristics may be restricted, thus limiting the corresponding data rate that the wireless terminal can reliably receive. Rate control for multicast services addresses this factor.
In the embodiment, wireless terminals 101, 151, 161, and 162 report corresponding measurements that are indicative of the wireless propagation characteristics by signaling base station 105 in the reverse direction of wireless channel 102. Wireless system 100 adjusts the configuration of wireless channel 102 in accordance with the measurements.
In the example, wireless channel 102 is logically partitioned into subchannels 171, 172, and 173 in which each subchannel transports a component of the multicast presentation. A subchannel is a logical or physical portion of wireless channel 102. The subchannel corresponds to a subset of the total data throughput of wireless channel 102. In the example shown in
With multicast services, the data rate on the downlink (forward direction) is substantially greater than the data rate on the uplink (reverse direction). The source of the multicast service comprises a stream of IP packets that are transported through IP core network 209, IP peer 211, an IP link 221, base station 105, and wireless channel 102. If wireless terminal 101 is served by base station 206, a data link 222 is utilized rather than data link 221 for transporting IP packets. In the exemplary embodiment, data links 221 and 222 are routed through node 207.
Node 207 acts as a layer 2 bridge between wireless terminal 101 and IP peer 211. (Layer 2 is the link layer in accordance with the Open Systems Interconnection (OSI) reference model. As a point of clarification, the term “layers” in reference to the OSI model is not the same as the term “layers” in reference to the transmission of multicast content.) Node 207 may have control functions as well as data plane functions. In some embodiments, node 207 can be implemented with a base station controller. Wireless terminal 101 periodically reports a measured signal to noise ratio (SNR) or similar quality measure using signaling messages from wireless terminal 101 to base station 105 over wireless channel 102 in the reverse direction at a low data rate. The SNR measurements are forwarded from base station 105 to node 207 over data link 225. If wireless terminal 101 is served by base station 206, then the corresponding SNR information is carried over a data link 227 to node 207. Node 207, as shown in
Node 207 converts an SNR measurement or a similar quality measure to a corresponding maximum data rate that wireless terminal 101 can support over wireless channel 102. Typically, the determination of the data rate for a time slot (as illustrated in
Data rate associated with SNR measurement
(corresponding to 1% PER)
Data Rate (kb/s)
With a variation of the exemplary embodiment, wireless terminal 101 may be associated with a quality of service (QoS) level in which the target PER is different than 1%, and thus may correspond to different values that are shown in Table 1. Different QoS levels can be assigned to different wireless terminals. (For example, a first QoS level may correspond to a target PER of 0.5%, and a second QoS level may correspond to a target PER of 1.0%.) In such a case, a corresponding maximum data rate to SNR mapping may be required.
With multicast services, wireless communications system 200 can simultaneously support a plurality of wireless terminals, each wireless terminal experiencing different radio propagation conditions as measured by the SNR. For example, at a given instant of time, wireless terminal 101 may measure SNR as −3.0 dB (which is between table entries for −1.0 dB and for −4.0 dB and thus corresponds to approximately 307.2 kb/s) while another wireless terminal may measure SNR as −10.0 dB (corresponding to approximately 38.4 kb/s). In such a case, wireless terminal 101 could process a signal at a data rate of 38.4 kb/s, but the other wireless terminal could not process a signal at a data rate of 307.2 kb/s. Because node 207 has SNR measurements about each of the plurality of wireless terminals, node 207 can group the plurality of wireless terminals in order to efficiently utilize the available frequency spectrum for multicast services. The example shown in
As can be appreciated by one skilled in the art, variations of the exemplary embodiment can support other variations of spread spectrum technology, including cdma2000 1X-EV-DV (1.25 MHz carrier-EVolution-Data and Voice) Standards and Universal Mobile Telecommunications System (UMTS) Standards.
Each wireless terminal (e.g. wireless terminal 101) is notified of assigned link-level multicast addresses as determined by the requested multicast service and the wireless terminal's SNR measurements. Each multicast service corresponds to at least one layer comprising layers G1, G2, . . . , Gm, where G1 may be a basic layer (e.g. layer 173 in
Ri is the data rate during a time slot as determined by the SNR measurement that is associated with the ith wireless terminal. Without loss of generality, the wireless terminals can be ordered according to the values of the associated SNR measurements. If there are n wireless terminals (MS1 to MSn), then:
The allowable data throughput for the ith wireless terminal is the sum of bandwidths corresponding to the layers that the ith wireless terminal can reliably receive. Thus, the allowable data throughput for the ith wireless terminal is T1+T2+. . . +Ti, where
B 1 +B 2 +. . . +B m1
The layers that the ordered wireless terminals can receive (as determined by the maximum data rate that can be reliably received by a wireless terminal and the total bandwidth for layers that are assigned to the wireless terminal) are:
first wireless terminal (MS1)⇄G1, G2, . . . , Gm1
second wireless terminal (MS2)⇄G1, G2, . . . , Gm1, Gm1+1, Gm1+2, . . . Gm2
ith wireless terminal(MSi)⇄G1, . . . , Gmi
Link-level multicast addresses are assigned corresponding to appropriate groups of layers, and consequently node 207 signals the wireless terminals (e.g. wireless terminal 101) about the assigned link-level multicast addresses. (One or more IP multicast layers can be transmitted during a time slot.) In the exemplary embodiment, a link-level multicast address is signaled to wireless terminals MS1 to MSn. If data is transmitted to link-level multicast address L1 during a time slot, the maximum transmission rate is R1. Because of the ordering of Ri's in EQ. 1, all wireless terminals MS1 to MSn can reliably receive the data. A link-level multicast address L2 is signaled to wireless terminals MS2 to MSn. This indicates that all wireless terminals MS2 to MSn should process data transmitted to link-level multicast address L2. If data is transmitted to link-level multicast address L2 during a time slot, the maximum transmission rate is R2. Because of the ordering in EQ. 1, it is always possible for all wireless terminals MS2 to MSn to reliably receive the data. However, MS1 does not process the data that is addressed to L2 because transmission rate R2 may be too high for MS1 to reliably receive the data. Precluding MS1 from receiving L2 also avoids the usage of battery power for processing data that may not be correctly decoded by MS1. This procedure is continued for the remaining n ordered wireless terminals as indicated in EQ. 1. In other words, all wireless terminals that are instructed to process a time slot can reliably receive (i.e. within the target PER) the data as determined by the SNR measurements associated with each of the wireless terminals.
The ordering of wireless terminals can be illustrated in the context of
wireless terminal 151→−11.0 dB
wireless terminal 161→−5.0 dB
wireless terminal 162→−4.0 dB
wireless terminal 101→4 dB
In the example, wireless terminals 161 and 162 are grouped together because both wireless terminals (161 and 162) can reliably receive layers 172 and 173 but cannot reliably receive layer 171.
Packets are scheduled from different layers over different time slots in accordance with the above process. Thus,
G1, . . . , Gm1→L1
Gm1+1, . . . , Gm2→L2
Gm(i−1)+1, . . . , Gmi→Li
Transmission over wireless channel 102 is scheduled as follows. If a time slot is allocated to wireless terminal MSi, the transmission during that time slot is addressed to link-level multicast address Li. The transmission is also received by wireless terminals MSi+1, . . . , MSn because wireless terminals are ordered by SNR measurements, i.e. MSi+1 has a larger SNR measurement than does MSi. (In other words, if MSi is able to receive at a given data rate, then MSi+1 is also able to receive at the given data rate.) The IP packet transmitted during this time slot is associated with the IP multicast layers that are mapped to Li. Of course, if a wireless terminal does not request a particular layer, even though the wireless terminal can reliably receive the transmission as determined by the above procedure, then the wireless terminal is not instructed about the associated link-level multicast address.
With a variation of the exemplary embodiment, the scheduling of packets may consider the QoS levels that are associated with MS1 to MSn. For example, the service provider may attempt to deliver packets to a group of wireless terminals (such as MS1 to MSn) in which a time delay or a variation of the time delay (typically referred as time jitter) has an upper limit set by the service provider.
The measured SNR at a wireless terminal MSi can change with user mobility. Thus, the ordering of wireless terminals can change with time, and consequently the above process must be updated accordingly. Moreover, wireless terminal MSi may wish to unsubscribe or subscribe to multicast services.
As an enhancement to the scheme described above,
In a state 401, node 207 obtains SNR measurements from wireless terminal 101 through wireless channel 102 and data link 225 on a repetitive basis. Upon receiving a new SNR measurement (corresponding to a trigger 407), node 207 determines predicted SNR (SNRp(t)) in a state 403. The exemplary embodiment utilizes exponential averaging:
SNR p(t)=a*SNR p(t−1)+(1−a)*SNR(t) EQ. 2
where SNR(t) is a SNR measurement from wireless terminal 101, and parameter a is determined according to local radio propagation characteristics. (EQ. 2 is referred as “exponential averaging” because the corresponding impulse function of the associated filter is an exponential function.) Variations of the embodiment can utilize other forms of averaging.
With a variation of the exemplary embodiment, movement detection may be incorporated into determining SNRp(t). As a variation of the embodiment, the SNR is predicted by:
SNR p(t)=a*SNR(t)+b*SNR p(t−1)+c*f(v,SNR(t)) EQ. 3
where a, b, and c are parameters that are dependent on local radio propagation characteristics, v is the estimated velocity of wireless terminal 101, and f is a function determined according to local radio propagation characteristics. In Equation 3, the predicted SNR is dependent upon the previously predicted SNR (SNRp(t−1)), the current SNR measurement (SNR(t)), and the movement (velocity, which includes speed and direction) of the wireless terminal as related by the function f(v,SNR(t)). In the embodiment, movement is determined by changes in the roundtrip propagation delay encountered on wireless channel 102. (If the wireless terminal is moving towards the serving base station, the SNR will tend to increase with time. On the other hand, if the wireless terminal is moving away from the serving base station, the SNR will tend to decrease with time. Also, the function f(v,SNR(t)) may be dependent on the SNR because time changes of the SNR are more pronounced during fades corresponding to small SNR measurements.
After determining SNRp(t), a state 405 is entered. Node 207 sends the measured SNR and predicted SNR to IP peer 211 through a data link 229. With a variation of the exemplary embodiment, node 207 notifies IP peer 211 about layers that can be currently supported by wireless channel 102. State 401 is re-entered in preparation to obtain a subsequent SNR measurement from wireless terminal 101.
In addition to message 801, wireless terminal 101 sends bandwidth requirements for each layer to the IP peer in message 803. Information about the bandwidth requirements are contained in memory of wireless terminal 101 and may be known a priori or may be obtained from a broadcast message that is transmitted over wireless channel 102. In the exemplary embodiment, the bandwidth requirements are contained in an extension of the IGMP message, although other embodiments can use a message or can utilize a data structure that associates bandwidth requirements with each layer.
IP peer 211 stores received information regarding membership to multimedia groups and the associated bandwidth for the layers. Message 803 may be physically separate from message 801 or may be physically included with message 801. With a variation of the exemplary embodiment, messages 801 and 803 comprise a consolidated message including IP addresses of multicast groups as well as associated bandwidth requirements. With another variation of the exemplary embodiment, a data structure is maintained at IP peer 211. The data structure associates bandwidth requirements with each multicast group (layer). The data structure can be provisioned with a priori information by the service provider or can be constructed with bandwidth information that is obtained from wireless terminals requesting multicast services.
IP peer 211 sends message 805 to inform node 207 about bandwidth requirements for each layer and to provide information about wireless terminal 101 joining the multicast session. Thus, node 207 obtains knowledge about the bandwidth requirements of each layer and about the set of wireless terminals (e.g. wireless terminal 101) that are participating in the multicast session. Subsequently, wireless terminal 101 sends a SNR measurement of the received signal on wireless channel 102 by sending message 807 through base station 105 to node 207.
Based upon the information obtained by node 207 in SNR measurement 807, node 207 determines the number of layers that wireless terminal 101 can reliably receive over wireless channel 102. (The procedure for determining the number of layers is described above.) (Variations of the embodiment may utilize other measurements, in lieu of SNR measurements, that are indicative of the radio propagation conditions.) Node 207 sends the number of layers to IP peer 211 in message 809. (Each layer is associated with a corresponding transmission bandwidth. The total bandwidth is the sum of corresponding bandwidths of each assigned layer. The total bandwidth should not exceed the maximum data rate corresponding to the measured SNR.) The transmitted signal transports streaming data for the multicast session and comprises at least one layer, with each layer corresponding to a link-level multicast address. In a variation of the exemplary embodiment, node sends the number of layers to wireless terminal 101 by sending message 808 through base station 105 in order that a display at wireless terminal 101 can be updated to show the user about the current status of the multicast service. The display will be discussed in greater detail in conjunction with
IP peer 211 utilizes information regarding the number of layers that can be supported on wireless channel 102 in order to control the rate of associated traffic through IP core network 209. With the exemplary embodiment, the data rate through IP core network 209 is adapted according to the data rate that wireless channel 102 can support. With varying radio propagation characteristics during the multicast session, layers can be added or dropped in response to SNR measurements from the wireless terminals that are participating in the multicast session. In the example shown in
If none of the wireless terminals can reliably receive a layer, then IP peer 211 can instruct an upstream IP router that the associated data (for the associated multicast group) can pause. Similarly, when at least one of the wireless terminals can reliably receive a layer over wireless channel 102, then the associated data stream can resume for the multicast group. The process for controlling the data flow through IP core network 209 is explained in more detail in conjunction with
Throughout the multicast session, wireless terminal 101 updates node 207 about SNR measurements of wireless channel 102 by sending message 811. Node 207 updates IP peer 211 and wireless terminal 101 about the number of layers can be received over wireless channel 102 with messages 813 and 815, respectively. The updating by wireless terminal 101 can be initiated by a number ways. In the exemplary embodiment, the message 811 occurs on a periodic basis according to a timer at wireless terminal 101; however, an alternative embodiment can utilize a threshold detector in which wireless terminal 101 sends message 811 only if the SNR measurement is below a threshold value.
If wireless terminal 101 wishes to leave the multicast session, wireless terminal 101 sends message 817 to IP peer 211. The appropriate membership information is updated. The tear down on the IP level can be executed either explicitly or implicitly. When explicitly executed, as shown in the exemplary embodiment, a dedicated message 819 is sent to tear down the connection for wireless terminal 101. (However, the data stream can continue for the remaining wireless terminals that are connected to the multicast session.) With implicit execution, wireless terminal 101 sends an IGMP leave message with the multicast group that is associated with the most significant layer of information, thus signifying that the connection is being terminated for wireless terminal 101. In such a case, IP peer 211 is aware of the semantics of the layers, i.e., which layer is the most significant for the multicast session.
In step 913, wireless terminal 101 requests a release connection (corresponding to message 817 in
In the exemplary embodiment, two IGMP message types are used to adapt the bandwidth of core IP network 209. If packets associated with a multicast group are not to be transmitted over wireless channel 102 (as determined by node 207), then a “PAUSE” message is sent to the upstream router (corresponding to router R1 601 in
Processor 1101 also obtains SNR measurements from wireless terminals in signaling messages (e.g. message 811) through I/O port 1105 and a link 1104. Processor 1101 stores the current SNR measurement from a wireless terminal, as identified by ID field 1111, into a field 1117 and the previous SNR prediction into a field 1119. Processor 1101 determines the maximum data rate from the SNR prediction, which is stored in a field 1121. Processor 1101 utilizes data structure 1123 through links 1122 and 1124 to convert the SNR prediction into the maximum data rate. Processor 1101 updates layers field 1113 according to the maximum data rate that the wireless terminal (associated with ID field 1111) can reliably receive.
Processor 1209 obtains multicast service requests from wireless terminals through IP ports 1203 and 1205. Each multicast session between a base station and a multicast content source corresponds to a connection. (A connection can support a plurality of wireless terminals that are served by a base station for a multicast service.) Processor 1209 determines configuration information (e.g. the number of layers that are being transmitted by base stations 105 and 206) and stores the information in a memory 1213 in fields 1221, and 1223. Processor 1209 instructs routing module 1201 to control the packet flow through IP core 209 in accordance with the information stored in field 1223. In the exemplary embodiment, routing module 1201 appropriately issues PAUSE and RESUME messages to upstream router 601. Embodiments of the present invention can incorporate the functionality of routing module 1201 into processor 1209.
As can be appreciated by one skilled in the art, a computer system with an associated computer-readable medium containing instructions for controlling the computer system can be utilized to implement the exemplary embodiments that are disclosed herein. The computer system may include at least one computer such as a microprocessor, digital signal processor, and associated peripheral electronic circuitry.
While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the appended claims.
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|U.S. Classification||455/454, 455/517, 370/232, 709/246, 709/231, 455/509, 370/233, 455/450|
|International Classification||H04L29/06, H04L12/18, H04L12/56, H04L29/08, H04L1/20, H04L29/12, H04W28/12, H04W4/06, H04W72/08|
|Cooperative Classification||H04L67/325, H04L69/329, H04L67/322, H04W28/12, H04L29/06, H04L61/00, H04L1/20, H04W72/08, H04L29/12009, H04L12/1836, H04L12/189, H04L1/0026, H04L1/0017, H04L2001/0093, H04W72/005, H04L1/0002|
|European Classification||H04W72/00B, H04L61/00, H04L29/08N31T, H04L29/08N31Q, H04L29/12A, H04L12/18W, H04L1/20, H04L29/06, H04L1/00A8Q, H04L1/00A1|
|Feb 20, 2002||AS||Assignment|
Owner name: NOKIA CORPORATION, FINLAND
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:TROSSEN, DIRK;CHASKAR, HEMANT M.;REEL/FRAME:012693/0487
Effective date: 20020215
|Oct 28, 2009||FPAY||Fee payment|
Year of fee payment: 4
|Oct 30, 2013||FPAY||Fee payment|
Year of fee payment: 8
|May 10, 2015||AS||Assignment|
Owner name: NOKIA TECHNOLOGIES OY, FINLAND
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:NOKIA CORPORATION;REEL/FRAME:035602/0257
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